An optical fiber preform is manufactured by, for example, (i) depositing SiO2 soot on a target via a VAD method or some other method and (ii) sintering the SiO2 soot thus deposited, in some existing techniques for producing SiO2 soot (see Patent Literatures 1 through 3, for example), SiCl4, which is a conventional source material of SiO2 soot, is replaced with organosilicon. The organosilicon is combusted in an oxyhydrogen flame (reaction field) with, use of a burner or other such apparatus so that SiO2 soot is produced. In comparison to SiCl4, using organosilicon is advantageous in that, for example, it avoids the creation of hazardous hydrochloric acid and requires less hydrogen than conventional methods.
In order to accelerate production of the SiO2 soot, an organosilicon source material needs to be supplied in great amounts. However, complete combustion of large amounts of organosilicon (concentrated organosilicon gas) is difficult. This causes a reaction of the organosilicon in the reaction field to be insufficient, thereby causing (i) impurity gel, impurity particulate, or the like to adhere to the burner (ii) carbon to adhere to the SiO2 soot, or (iii) formation of imperfections in the SiO2 soot. In order to address issue, the organosilicon is premixed with an oxygen gas prior to combustion in order to improve reactivity of the organosilicon.